Hook-and-loop fasteners are widely used as garment fasteners. Commercial examples of these fasteners include those marketed under the VELCRO brand by Velcro USA Incorporated and under the SCOTCHMATE brand by Minnesota Mining and Manufacturing Company, St. Paul, Minn., which fasteners are made by a variety of methods. Early versions of the hook materials still available today are taught in U.S. Pat. Nos. 2,717,437 and 3,009,235 (both by DeMestral), where a hook strip is made from specific warps of upstanding nylon loop pile. One leg of each loop is cut to leave an open-ended J-shaped hook, which is available to act as a fastening element.
U.S. Pat. No. 3,594,865 (Erb) describes an injection molding technique for manufacturing a J-shaped hook strip of a hook-and-loop fastener. The technique taught is the use of a closed "loop material" having a large number of separate shallow "wire dies" formed in the loop material. While applying a vacuum to evacuate the "wire dies", the closed loop is passed through an extruder which forces molten plastic, such as nylon, into the dies while also impregnating a fabric web immediately beneath the loop material. Upon exiting from the extruder, excess resin is stripped from the surface of the wire dies. The resilient hooks then come progressively out of the dies, providing an orderly array of hooks projecting from a plastic impregnated fabric web. Instead of using a fabric web, the apparatus can be modified to create a space beyond the wire dies into which the molten plastic can flow to form an all-plastic backing for the hooks. Another U.S. Pat. No. 3,594,863 (Erb) relates to similar apparatus for producing a similar hook-bearing strip. These patents state that the disclosed method can produce a wider variety of shapes than a traditional solid die which is limited to shapes that taper from base to tip. However, this method would likewise be limited to shapes that must taper inward except in this case, from one outer face to an opposing face along the length of the hook. It is also difficult to impregnate the polymer in the supporting fabric behind the "loop material".
In U.S. Pat. No. 3,718,725 (Hamano), the hook strip fastener of a hook-and-loop mechanical fastener is made from a fabric having an orderly array of upstanding loops. After inserting rods into rows of loops to maintain their upstanding position, platens or rollers apply heat and pressure to melt each loop at its summit and to press each free molten end to form a knob or head that can inter-engage with the loop strip of a hook-and-loop fastener. Because the knobs or heads have a mushroom appearance, this type of hook fastener is called "mushroom-type".
Mushroom-type hook fasteners are sometimes designed so that two like hook strips can be fastened together. Such self-mating types of mushroom-type mechanical fasteners are shown in U.S. Pat. No. 3,192,589 (Pearson) which calls the fastener "hermaphroditic" because its headed studs have both male and female characteristics when intermeshed. The Pearson fasteners can be made by molding a base from which integral headless studs project and then heat softening the tips of the studs.
The hermaphroditic mushroom-type mechanical fastener shown in U.S. Pat. No. 4,290,174 (Kalleberg) is made with flexible, resilient, U-shaped monofilaments. The "central bight portion" of each monofilament is embedded in a flexible bonding layer so that two stems of the monofilament project normally from the surface of the bonding layer. There is a mushroom head at the tip of each stem formed by heating the terminal ends of the monofilaments, preferably formed of a polyolefin. The stems preferably are substantially uniformly spaced and of substantially equal length. Maximum disengagement force is achieved when the spacing between adjacent heads is less than their diameters and the minimum required for engagement.
U.S. Pat. No. 3,408,705 (Kayser et al.) also shows mushroom-type mechanical fasteners having mushroom heads of several shapes. The "globe-shaped" (e.g., mushroom-shaped) heads are formed by heating cylindrical stems. J-hook shaped heads are formed by heating stems with wedge-shaped terminal ends.
Another procedure for continuously molding a J-shaped hook strip is described in U.S. Pat. No. 3,762,000 (Menzin et al). The process uses mold plates with cavities for molding upstanding J hook members or pile-like formations. The moldable plastic material is applied in two steps, first under high pressure to form the J hook-shaped pile-like formations while still in the cavities and secondly under lower pressure to form the strip constituting a base member so that the J hook-type protuberances are integrally attached. U.S. Pat. No. 5,260,015 (Kennedy et al.) alters the Menzin et al. molding process by adding processing steps to firmly bond a backing material to the molded J hook-type extruded hook fastener strips.
U.S. Pat. No. 4,984,339 (Provost et al.) discloses a molded J-shaped hook which has a profile defined by an inner smoothly contoured, generally concave face and an outer, generally convex face. The hook tapers smoothly and continuously downward in width from a sturdy base member to a free end. The hook is designed so that it will not deform to release a loop engaging the hook in shear at or below a desired applied force.
U.S. Pat. No. 5,315,740 (Provost) discloses a molded hook shaped like that in U.S. Pat. No. 4,984,339 which is designed for use with a low profile loop closure system. A displacement volume is determined for the hook which is defined, generally, as a rectangular parallelepiped surrounding the hook tip.
There still exists a need for an improved method for making J hook-type hook strips without using time consuming and complicated molding processes to create J hook-shaped stems on a backing material.